Model Description

This model describes the minimal realisation of the Type III seesaw. It is an extension of the Standard Model where a fermionic SU(2) triplet is added to the matter content in order to give mass to one neutrino via a seesaw mechanism. The fermionic triplet is introduced under the form of a heavy Dirac charged lepton tr+/- and a heavy Majorana neutral lepton tr0. For an exhaustive description of the model, see references below.

Model Files

For MadGraph/MadEvent and BRIDGE users: ​formats.inc: this is a modified version of the file formats.inc, that can be useful when dealing with small mixing angles (the original file sets to zero couplings smaller than 10-5)

typeIIIseesaw.nb: this is an example of the Mathematica notebook that loads the model, performs few checks, and export it to the MadGraph and CalcHep format.

Validation

In order to validate the implementation of the model we have checked several processes:

We also checked the compatibility of our model with Madgraph version 4 and version 5.
(N.B.: when running this model with mg4 some channels are not generated. Please, use mg5 to have the correct result.)

Notes

We implemented the couplings to Goldstone bosons so that the implementation allows for the use of the Feynman gauge. We have checked that the exportation to the CalcHep format is successful, however we did not check the CalcHep output.

N.B.: when using this model with CalcHep the variables (such as input parameters) longer than 6 characters must be redifined to shorter words (thanks to Jayash Panigrahi).

COMMENTS TO THE VARIOUS VERSIONS:

1.1: "IndexRange[ Index[SU2W] ] = Range[3]" has been substituted by "IndexRange[ Index[SU2W] ] Unfold[Range[3]]" , in order to get UFO output. If you do not need them, you can use the 1.0 version.